This makes its way through to the API level. For example, in Unix, there are certain devices you can do an fseek() on (i.e. a move to a random location), such as hard disks, and others that you can not (e.g. serial ports).

Random Access Memory is named so because you can read any address you like at any time, You don't need to do it in a particular order. There was a time when memory wasn't random (e.g. stored on a magnetic drum, or using mercury delay lines).